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The periosteum is a membrane that covers the outer surface of all bones, [1] except at the articular surfaces (i.e. the parts within a joint space) of long bones. (At the joints of long bones the bone's outer surface is lined with "articular cartilage", a type of hyaline cartilage.)
Cortical bone is covered by a periosteum on its outer surface, and an endosteum on its inner surface. The endosteum is the boundary between the cortical bone and the cancellous bone. [11] The primary anatomical and functional unit of cortical bone is the osteon.
The cortex of a bone is used to refer to its outer layers, and medulla used to refer to the inner surface of the bone. Red marrow , in which blood is formed is present in spongy bone as well as in the medullary cavity , while the fatty yellow marrow is present primarily in the medullary cavity.
This is covered by a membrane of connective tissue called the periosteum. Beneath the cortical bone layer is a layer of spongy cancellous bone. Inside this is the medullary cavity which has an inner core of bone marrow, it contains nutrients and help in formation of cells, made up of yellow marrow in the adult and red marrow in the child.
This endosteal surface is usually resorbed during long periods of malnutrition, resulting in less cortical thickness. [3] The outer surface of a bone is lined by a thin layer of connective tissue that is very similar in morphology and function to endosteum. It is called the periosteum, or the periosteal surface.
Diagram of a typical long bone showing both compact (cortical) and cancellous (spongy) bone. Osteons on cross-section of a bone. In osteology, the osteon or haversian system (/ h ə ˈ v ɜːr. ʒ ən /; named for Clopton Havers) is the fundamental functional unit of much compact bone.
Most bones of the calvaria consist of internal and external tables or layers of compact bone, separated by diploë. The diploë is cancellous bone containing red bone marrow during life, through which run canals formed by diploic veins. The diploë in a dried calvaria is not red because the protein was removed during preparation of the cranium.
These blood vessels will eventually develop into red bone marrow. Mesenchymal cells on the bone surface form a membrane known as the periosteum. Osteoblasts secrete osteoid in parallel with the existing matrix, creating layers of compact (cortical) bone. [4]